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Gas Milage? What happened from '89 to '01?

B

bobblead

NAXJA Forum User
Location
San Diego
I had a 1989 Cherokee Laredo totally stock 2x4 automatic 4.0L. I put 270,000+ miles on it. Regularly got 20 mpg on mixed freeway and city driving, or about 340 miles per tank of gas.
Given my great experience when I had to give up the Laredo because of an accident, I bought a 2001 Cherokee Sport, same 4.0L engine automatic transmission, 2x4. I get maybe 16mpg if I'm lucky.

What happened?
 
I also wonder about this. I have read many threads about gas milage and those with older vehicles seem to get better milage. WHY? My '01 will pretty much never get 20 mpg.
 
well i'm ignorant with this, but i'm gonna suggest maybe the increases in power over the years changed the gas mileage

have you checked your o2 sensors? how old is the cat? plenty of other factors at work here

i avg. 19 mpg in my '01 4x4
 
Fred85 said:
well i'm ignorant with this, but i'm gonna suggest maybe the increases in power over the years changed the gas mileage

have you checked your o2 sensors? how old is the cat? plenty of other factors at work here

i avg. 19 mpg in my '01 4x4
Click to expand...

Me 2. But like the teevee ads say, "YMMV"
 
Fred85 said:
well i'm ignorant with this, but i'm gonna suggest maybe the increases in power over the years changed the gas mileage

have you checked your o2 sensors? how old is the cat? plenty of other factors at work here

i avg. 19 mpg in my '01 4x4
Click to expand...

How about driving style? My stock '00 4x4 just got 22mpg on my last tank, but I drive it like a senile old man (easy on the gas around town, speed limit on the highway). Used to drive it more aggresively and was getting 16-18mpg.
 
I do notice a difference between my 90 and 92. Having said that, I will say that my 90 has the best performance and milage since I replaced the injectors at 180K. Better than new. OK I do have k&N + complete Borla exahaust with high flow cat, but even after the injector change, it is the best ever.
 
My wifes 2000 4x4 just got 18-20 for the week in Colorado and on the way home, that included several hours in 4low. Once we were in Dallas at her brothers house it dropped to about 15-16. Different fuels, and air density changes have a HUGE effect on mileage
 
Ive got two 1992 lerado with AW4's XJ's and a 1997 XJ with AW4. The two 92's get way better gas milage than my 97. And the 92 Xj's are peppier!!! Same motors same trannies same gears same tires. 1 for me, 1 for my wife and 1 that is the well just an extra one.
 
A MAJOR factor that comes into play is where at in the country you live. I live in southern Louisiana, where humidity is a year round thing. I have a 1998 GMC Z71 with the 5.7L. I get 16MPG mixed. I took a trip out to AZ last summer and stayed there for about 2 weeks. I got about 20MPG. Same driving style and everything.

That moisture in the A/F ratio will kill both power and efficency.

Daniel
 
bobblead said:
I had a 1989 Cherokee [...] Regularly got 20 mpg on mixed freeway and city driving. I bought a 2001 Cherokee Sport, same 4.0L engine automatic transmission, 2x4. I get maybe 16mpg if I'm lucky.

What happened?
Click to expand...

The '89 has a disco front axle... put there by AMC to increase fuel economy... removed by DC to cut costs, and increase reliability.

The '00 has quite a bit more horsepower.

The '00 probably has wider tires.

The '00 transmission is hard-wired into the "power" mode of the 89's Power/Comfort switch.

The '00 likely has a beefier alternator, and perhaps AC condensor... each will use more power... at least when in operation.

The '00 has several safety upgrades that would probably add weight - dual airbags, side door beams, etc... as well as beefier U-joints and some other stuff.

Also, though it only affects cold-starts... I seem to recall that one of the modernizations of emission controls (perhaps when OBD-II was adopted?) there was a loosening of the cold-start emissions requirements. This allowed the manufacturers to tune the engine a little richer during cold starts, to help with smoothness and power. If a fair amount of your time is spent on short trips, this could make an appreciable difference. (If it happened. I certainly REMEMBER it happening...)

Den
 
i know my mpg went down a bit changin my front end 90 dana 30 to a 98 because of the lack of discos, every little bit can make a differance
 
glub said:
Tailgate must be heavier seeing it's not fibreglass..
Click to expand...
not necessarily

fibreglass is not inherently lighter. Sometimes properly engineered fiberglass structures can be lighter than steel. sometimes the other way around. I have built boats to the same design out of steel, fiberglass, wood/epoxy. foam cored fiberglass was a little bit lighter than the steel but solid laid fiberglass was heavier, and not as stiff. the stiffest, lightest, and on paper at least, strongest were the wood/epoxy hulls.

I have never hefted the steel hatch but i can tell you that the fg one is way heavier than i would have built it.



caveat
the wood/epoxy got a skin of one layer of 8oz fiberglass cloth wetted out with epoxy. Noone would call them tupperware as it is mostly just for abrasion resistance
 
My 1990 with 4.0/AW4/231 (Renix electroics) gives 2 to 3 mpg better mileage on the highway than my 2001 with 4.0/AW4/242 (Chrysler electronics). The 1990 has more than double the miles on it, but I like it better in a number of ways. I did pick up 1 to1.5 mpg by replacing the rusted-out OEM muffler with a low restriction stainless steel Dynomax muffler, at only a modest increase in noise over stock Good deal!
 
Ok, here is one for thought, i work with a 3 other guys with jeeps, and talking over break with them all lined up in the lot we could not figure the whole mpg thing out either.

I have a 97 xj with a 3in lift and 31s and a roof rack, i get 16 driving nice down the road, and about 12 mixed. I have stock gears, and i know my muffler is getting bad, and cat is not tight on the pipes anymore (projects for this week end).

One of the others has a 95 xj, bare bones stock, street tires, no gearing differences, just stock. he gets 22 highway, 16 mixed.

Then a 02 TJsport (CJ5?), 31s factory, but no lift at all, 15 is the best he can get.

Then the other is a 95 GRAND Cherokee, stock with 4.0 auto, and he gets 28-30 on the highway.

We all got to looking, and we all have between 120K and 150K, same motors, same trans, all 4wd, all with stock diff gears, and such a change in milage. We could not figure it out.:confused:
 
NighthawkXJ said:
Ok, here is one for thought, i work with a 3 other guys with jeeps, and talking over break with them all lined up in the lot we could not figure the whole mpg thing out either.

I have a 97 xj with a 3in lift and 31s and a roof rack, i get 16 driving nice down the road, and about 12 mixed. I have stock gears, and i know my muffler is getting bad, and cat is not tight on the pipes anymore (projects for this week end).

One of the others has a 95 xj, bare bones stock, street tires, no gearing differences, just stock. he gets 22 highway, 16 mixed.

Then a 02 TJsport (CJ5?), 31s factory, but no lift at all, 15 is the best he can get.

Then the other is a 95 GRAND Cherokee, stock with 4.0 auto, and he gets 28-30 on the highway.

We all got to looking, and we all have between 120K and 150K, same motors, same trans, all 4wd, all with stock diff gears, and such a change in milage. We could not figure it out.:confused:
Click to expand...
Accually they're nothing the same in the compairson. The TJ, and the ZJ have different trannys (both 42RE"s IIRC). The TJ is less airodynamic than an XJ, and the ZJ is more. Your XJ is less airodynamic than the stock one due to the lift, and rack.
 
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